Transformer



June 19; 1945.

C. E. SEIFERT TRANSFORMER Filed June; 20, 1940 4 Sheets-Sheet 1 Invenior aimzes E. Safari,

June 19, 1945. c, E, SEIFE'RT 2,378,884

TRANSFORMER I 4 Sheets-Sheet 2 Filed June 20, 1940 b 6 IMJW, I

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0. E. SEIFERT TRANSFORMER June 19, 1945.

4 Sheets-Sheet s Fil ed June 20, 1940 Invenior: Charles E. *Sezjeri,

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June l9, 1945. c. E. senm TRANSFORMER Filed June 20, 1940 4 Sheets- Sheet 4 K 1717/621207'. Charles E S l w, 0 by 5M, 4M, I

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Patented June 19, 1945 TRANSFORMER Charles E. Seifert, Swampscott, Mass., asslgnor to Thomson-Gibb Electric Welding Company,

Lynn, Mass., a corporation of Massachusetts Application June 20, 1940, Serial No. 341,489

11 Claims.

This invention relates to electric transformers and more particularly to those employed for resistance welding where large volumes of secondary current are required for brief intervals in the welding operations.

One object of the invention is to increase the efliciency of the transformer and to reduce the demand made on power lines from the use of such transformer, while at the same time still securing the large volumes of secondary current as are called for.

In the use of such transformers, due to the reactance of the entire circuit, the primary current input required to secure the necessary volume of secondary current is apt to be very high, causing a serious voltage drop in the power line when the welding or secondary circuit is closed. This results in wide fluctuations in the voltage in the power line which are difficult and often impractical to control at the central station This voltage drop is due in part to the resistance and reactance 'of welding circuit outside of welding machine which are fixed and un'changeable. The leakage reactance in the transformer itself, however, contributes materially tothe reactance of the circuit as a'whole and-to the drop in the voltage at the terminals of the transformer when under load;

When the current flows through the primary of the transformer it magnetizes the transfomier core and the pulsating flux induces a current in the secondary winding opposite in phase to that of the primary current. These opposing currents tend to set up a leakage flux, a part of which returns through the iron core of the transformer and part through the air space between the primary and secondary coils. This leakage flux materially reduces the open circuit'or no-lo'ad terminal voltage of the transformer when it is placed under load.

Leakage between the primary and secondary coils, however, is not confined to the air gap between the coils but some of this leakage flux passes through the copper windings themselves. This tends to set up eddy currents in the windings, serving only to heat the copper and further increase the voltage drop on closed circuit.

. The reactance in a transformer increases with the thickness in an axial direction of both the high and low voltage coils or groups of coils, with the distance in an axial direction between the centers of high and low coils or groups of coils. and also with the square of the number of high voltage turns effective in establishing leakage flux across any one leakage path The present invention is designed to provide the closest practical approach to an ideal condition in respect to eachof these factors, bringin the reactive drop in the transformer to a minimum. Thi is accomplished by providing both high and low voltage coils of the maximum possible thinness, interleaved in close compact faceto-face relation to reduce the distance between coil centers, and with a minimum number of high voltage turns interleaved with each low voltage turn, which latter are connected in multiple. This makes it possible greatly to lessen the reactance and to increase the aggregate number oi primary turns in inductive relation to the secondary, thereby to increase the transformation ratio and provide the required volume of secondary current with a greatly reduced input amperage. This will be evident for the amperes multiplied by the number of turns must be the same in both the primary and secondary windings, and, since there is but one effective turn in the secondary, increasing the aggregate number of primary turns reduces the needed primary amperage.

This object is secured by providing the primary windings in a. plurality of serially connected sections, each section consisting of a minimum number of turns each in the form of a relatively wide thin flat conductor wound. edgewise; and further providing secondary turns which may be connected in multiple, each secondary turn being also in the form of a relatively wide thin flat conductor and also wound edgewise, one secondary turn being interleaved between each two adjacent primary sections and in close compact faceto-face relation with the primary turns, separated only by the necessary intervening insulation. Both the primary and secondary windings may be wound edgewise to form windings of a generally rectangular or other polygonal shape or of a generally circular shape.

The use of relatively wide fiat conductors, wound on edge, for the primary and secondary coils and arranged and interleaved as indicated not only greatly reduces the reactance, but since the intersecting flux can out only the relatively narrow edges of the windings the eddy current losses in the windings are greatly reduced.

conductive metal;

Fig. 3 illustrates the first step in the formation of the primary windings;

Fig. 4 illustrates the next succeeding step;

Fig. 5 is a perspective illustrating how a single secondary leg is interleaved with successive primary turns;

Fig. 6 shows the relation of the primary and secondary windings, which are here spaced apart for clarity, and with the cross-over connections between successive primary turns shown diagrammatically;

Fig. 7 is an elevation showing the transformer with the windings assembled on the core, looking in a direction transversely the windings;

Fig. 8 is an elevation of the transformer lookin in a direction lengthwise the windings;

Fig. 9 shows in side elevation another transformer, embodying the same principles but in which windings are formed from heavier strips or plates of copper;

Fig. 10 is a plan view showing the relation of the windings in the transformer of Fig. 9;

Fig. 11 is a detail showing in side elevation one of the secondary legs or turns for the transformer shown in Fig. 9;

Fig. 12 is a cross-section of the secondary leg, taken on the line l2-l2 in Fig. 11, where the leg is formed of several strips;

Fig. 13 shows one method of forming the secondary leg by use of inner and outer concentric strips;

Fig. 14 is a cross-section on the line I 4- in Fig. 13, illustrating a difference in the cross-section of the inner and outer strips;

Fig. 15 shows in elevation one section of the primary windings of the transformer of Fig. 9;

Fig. 16 is a plan view of a primary winding section;

Fig. 17 shows in plan a section of the windings of a transformer similar to that of Figs. 9 and 10, but with the back of each secondary leg provided with a water cooled fin;

Fig. 18 is a side elevation showing the water cooled fin for one of the secondary turns; and

Fig. 19 is a section in plan on the line I 9-49 in Fi 18.

Referring to the drawings, and first to Figs. 1 to 8 inclusive, there is shown for illustrative purposes one embodiment of the invention in which both the primary and secondary turns are formed of relatively wide fiat strips of conductive metal,

. such as copper, of such thinness that their flat faces are capable of being bent and folded.

In this case, the secondary legs of the transwhen taken in connection with the accompanyturns are formed from a similar but longer strip of flat thin copper. In forming the primary turns, one end of the strip (Fig. 3) is first bent along the diagonal lines of fold l3 and I5, as described in connection with Fig. l, leaving an extension H which serves as one primary terminal.

The other leg of the strip is then bent upward about the line of fold I9, as indicated in Fig. 3. Next, as shown in Fig. 4, the upstanding continuation of the strip is bent along the diagonal line of fold 2|, thereby forming one complete turn of the primary winding which consists of the upper and lower strips 23 and 25 and the side strips 21 and 29.

Successive steps of this operation are then repeated over and over again, bending the continuous strip to form a series of similar turns. The

primary winding, when completely formed,-as-.

sumes the shape shown in Fig. 2, with the ultimate end 3| of the strip forming an extension parallel to the extension I! to serve as the remaining primary terminal.

The primary winding when completed presents a continuous flat-sided winding on edge (Fig. 2) enclosing a polygonal and herein rectangular core space 33, the successive turns of which can be opened up or separated like the helices of a spring to permit the interleaving by insertion between successive turns of the separate secondary legs.

The windings having been thus formed, the strips constituting the secondary legs are covered with any suitable thin insulating material such, for example, as glass tape. The primary windings may be similarly insulated, but where a secondary is disposed between each two adjacent primary turns, the primary insulation may be unnecessary since the insulated secondary separates one primary tum from another.

To interleave the windings each secondary leg is inserted into the nest of primary turns, one to lie between two adjacent primary turns, the next to lie between the next adjacent primary turns, and so on. This may be accomplished by interleaving the secondary leg between two adjacent primary turns, as illustrated in Fig. 5, so that the upper strip 1 of the secondary leg lies between the strips 23 of adjacent primary turns, the lower strip 9 of the secondary between the strips 25, and the cross strip ll of the secondary between side strips 21, but with the side strip 29 of one primary turn to the next turn passing from one side of the secondary strip 1 to the opposite side of the secondary strip 9. This leaves the side strip 29 of one primary turn crossing from one side of the secondary leg to the opposite side thereof and serves as a cross-over connection for the adjaformer may each be formed, as shown in Fig. 1,

Any desired and suitable number of primary cent primary turns in the open space of the secondary leg. Each complete primary turn thus constitutes a primary winding section with a secondary turn interleaved between adjacent primary winding sections and, when finally assembled, are in close compact face-to-face relation separated only by the intervening insulation.

This interleaving assemblage of the primary and secondary windings provides one secondary turn placed face-to-face compactly between each two adjacent primary turns, with all the primary turns serially connected and with the closest possible relation between the windings. This leaves the successive primary and secondary turns in a relationship which may be diagrammatically represented in Fig. 6, but where the primary and secondary turns for clarity are shown spaced one from another, the primary turns being represented at 35, the secondary legs at 31 and the cross-over connections between successive primary turns at 35.

The windings after assemblage in a compact face-tofaoe relation are mounted in a laminated iron core ll of any usual or suitable construction, having (Figs. 7 and 8) the winding core member 43 of rectangular cross-sectionto tlt the core space 33 in the windings. turns are connected in multiple to terminal headers (not shown) by bolting or brazing all the extensions 1 of the secondarylegs to one terminal head of the welding circuit and the extensions 9 to the remaining terminal head. The extension H of the primary winding is connected to one terminal of the line and the extension 3| to the other terminal thereof, so that all the primary windings are in series.

While the optimum condition is reached by compactly interleaving one secondary winding leg between each two successive primary turns, certain advantages of this type of transformer winding may be had by so interleaving the secondary legs that they are opposed in compact face-to face relation each to a group of two or more serially connected primary turns.

The number of primary and secondary turns will, of course, be selected according to the ratio of transformation desired, and this ratio may be varied by dividing the serially connected primary turns into groups, which groups in turn are connected in multiple.

The described method of forming the windings may be employed where copper in strip form is used of a thickness which permits the bending and folding described. By way of example, a transformer suitable for lower capacities in welding work may be constructed by this method using copper strips for the windings from i to 4 inches wide and approximately .010 to .056 inch thick.

Since the thickness of the primary and seccndary turns. the distance between their centers and the number of primary turns effective in establishing leakage flux across any one leakage path have been reduced to a minimum and the primary and secondary windings are presented to the intersecting flux in a most efiective relation for preventing eddy current losses, the leakage reactance in the transformer is reduced to a minithe number of primary turns can be increased and the same current volume may be secured in the welding circuit with a. reduced cur rent volume in the primary.

In larger capacity units, welding currents of very large volume may be called for, requiring a i cross-sectional area in the windings inconvenient or impracticable to secure with flexible copper strips. Or for mechanical reasons it may be impracticable to construct the primary in the form of a continuous helix. In this case substantially he same principle may be utilized by employing thicker strips of copper or other conductive metal wound or bent on edge about suitable forms or arbors, the secondary turns being formed each into a flat horse-shoe or hair-pin shape, and the primary winding being formed into separate -sec tlons each of which comprises one or more complete turns.

One transformer or this type isillustrated in Figs. 9 and it. In this case (Fig, 11) the secondary turns 4? comprise each a relatively wide flat copper strip which, for example, might be of an inch thick and several inches in width. This is formed into'a flat horse-shoe shaped leg, as shown in Fig. 11, by being bent on edge about The secondary a suitable form or arbor, after which it may be covered with thin insulating tape 48 (a portion only of which is shown), which however preferably terminates short of the projecting ends BI and 53 of the leg so as to leave the bare metal of the latter exposed to the air.

Where the combined width and thickness of the secondary leg called for by current requirements make it difllcult to bend the copper on edge as described, the. secondary leg may be formed of two or more thinner copper strips 41a, 41b, 41c, etc., as indicated by the cross-section in Fig. 12', which are then taped together so that they act as one solid section or a composite con ducting leg.

The current carrying capacity of the secondary leg may furthermore be increased, if desired, by increasing the width of the secondary leg. If the width is increased to the point where mechanical dimculties are encountered in bending the strip, the leg may be formed in two parts, as shown in Fig. 13. Here the leg is made up of an outer strip 41d bent about one arbor and an inner strip 410 bent about another and smaller arbor but closely interfitting within the outer strip. The secondary turn then comprises inner and an outer fiat strip each wound on edge and arranged concentrically one within the other. The two parts may then be taped together and function as one single section. In this case both the outer and inner strips Nd and He may be formed from two or more laminated copper strips, as illustrated in Fig. 12.

Where an inner strip is employed arranged concentrically within an outer strip, as illustrated in Fig. 15, the outer strip which presents the longer path to the current may be made of somewhat greater thickness than the inner strip, as

indicated in Fig. 14, thereby to equalize the current flow and the heating effect of the current throughout the secondary turn.

The primary turns are also formed of thin i'lat strips 55 of copper of a width corresponding to the width or the secondary turns. As in the case of the secondary legs, the turns of each primary section may be formed from a single strip or made up of laminated strips face-to-iace, as in Fig. 12, or built up of concentric inner and outer strips, as in Fig. 13, or the methods both. I ig. l2 and Fig. 13 may be employed, as well as the use (Fig. it) of inner and outer turns of differ ent thickness.

it will be observed that whether a secondary or a primary turn is formed from a single stripof conductive metal, or is or composite forma tion, as through the use of laminated strips, or concentric inner and outer members, any one conductive turn is not only wide, thin and hat but the part or parts of which it is composed function as a single conductor. It is accordingly intended to include within the term of wide thin flat conductive turns both those composed of a single strip and those or composite formation.

acting as a single conductor.

In the case of primary windings, each section is formed by bending the strip about a suitable arbor so that it assumes the helical form shown in Figs. 15 and 16, the winding being provided preferably with one or more completeturns. The strip terminals 5? and 59 are left project ng tangentially from the section, as indicated in Figs. 9. and 15, and the terminals 59 are bent laterally into such a position (Fig. 10) that a series connection from one primary winding section t'o'another can be readily made.

The helical strip constituting each primary section is insulated as by being wound with thin insulating tape 55 (a short length only of which is shown), which however may be applied to leave uncovered and exposed to the air the bare metal of the projecting tails or terminals 51 and 59.

Each section of the primary windingmay be wound in a number of helical turns, but this number is preferably kept as low as practicable for each section, preference being that they should not exceed two or three turns, thereby providing a relatively large number of very thin fiat primary sections, each of a low number of turns, between adjacent sections there being interleaved a single secondary turn in close compact face-to-face relation to the primary turns. In the case of the primary section illustrated in Figs. 15 and 16, the primary winding of each section has somewhat less than three complete effective turns formed from the flat coils wound on edge and compactly arranged side by side.

In the transformer, the primary sections and secondary legs are mounted in the core 6| having the winding core member 63, indicated in Fig. 9'

but omitted for simplicity from Fig. 10. On the core they are assembled, as shown in the drawings, with one secondary leg (Fig. 10) interleaved between each two adjacent primary sections, with the broad, flat sides of each thin secondary turn in close compact face-to-face relation with the corresponding broad, flat sides of the adjacent insulated thin primary sections. If desired the insulation may be omitted from the secondary turns.

The projecting terminal ends 5| and 53 of the secondary legs project from the core in one direction, the ends of the upper legs 5| being seated and brazed in spaced recesses of one terminal head 65 of the weldin circuit and the.

ends of the lower legs 53 similarly connected to the underlying other terminal head 61 of the welding circuit, thereby connecting all the sec-' ondary legs in multiple. The terminals 51- and 59 of each primary section project from the opposite side of the core, preferably extending for a substantial distance at one side of the transformer and clear of the compactly related secondary turns. The terminal 59 of one section is bolted or otherwise connected to the terminal 51 of the next adjacent section to provide a series connection for the entire group of primary sections. Connection to one side of the line circuit is established through the terminal 51 of the end primary section of the group and connection to the opposite side of the line circuit through connection to the terminal 59 at the opposite end of the group.'

This arrangement of the primary and secondary windings, provided each with wide fiat conductors wound on edge and interleaved in close compact face-to-iace relation with one secondary turn between eachadjacent primary sec-- tion; provides a close approximation to the conditions described in connection with the transformer in Figs. 1 to 8. Furthermore, it provides a highly important condition of greatly enhanced cooling capacity for the transformer as a whole. The primary coil sections being' wound in comparatively few turns, the tendency for th production of hot spots is greatly reduced since there is relatively little insulation for the heat to pass through. Copper beinga good heat conductor, the heat generated in the turns can readily escape lengthwise the relatively short intervening path to th wid flat exposed extensions 51 and 59 which provide the series connections from section to section.

These extensions each presents a heat radiating or conducting surface relatively large in proportion to its cross-section, and the group as a whole, comprising two extensions or tails for each primary section, each exposed to the air, is capable of rapidly dissipating the heat conducted to them. Similarly, the bare exposed extensions 5| and 53 of the secondary windings, being also exposed to the air, contribute their effect to the further dissipation of heat..

The natural dissipation of heat from the primary and secondary extensions may be increased by forcibly blowing air or circulating other cooling medium over either or both, or by immersing them in a cooling tank suitably arranged to enclose them, or the entire transformer might be immersed in a tank of oil for cooling it. Additional cooling means might be applied to the secondary windings by circulating cooling water through passages in the terminals 65 and 61.

In Figs. 17 to 19 inclusive there is shown an effective cooling means for the secondary turns, the use of which is facilitated by this method of arranging and interleaving the windings.

This is accomplished by attaching to the secondary leg 41, intermediate its terminals and preferably at the mid portion of its curved back, a rearwardly projecting copper or other metallic cooling fin ll of substantially the same thickness as that of the le and having its attached edge curved tomate with the curved outer edge of the leg. This attachment is preferably by brazing the metal of the fin to the metal of the leg so that it becomes in effect an extension of the metal of the leg.

This fin is herein provided with an internal chamber 13 through which a cooling medium, such as cold water, may be circulated, entering through one pipe, such as the pipe 15, at the bottom of thefin from any suitablesource (not shown) and being discharged through another pipe, such as the pipe 11, at the top of the tin. These fins may be made to present a large crosssection for heat conduction from the secondary and a broad internal area exposed to the cooling water for the effective abstraction of conducted heat. In the illustrative example they assume such a form as to provide a large rectangularly shaped cooling chamber. The heat generated in the secondary leg is rapidly conducted to the projecting fin and abstracted therefrom by the circulated cooling water or other cooling medium.

The primary and secondary turns are assembled as previously described and as indicated in Figs. 17 and 18. There is shown in Fig. 17 a group of five primary sections, but this is merely illustrative and it will be understood that any desired number of primary sections may be employed to secure the desired ratio of transformation, there being a secondary turn between each two adjacent primary sections. As before, the flat thin secondary legs are interleaved, one between each thin fiat primary section, in close face-to-face compact relation. This also compacts each fin, or a large part of it, between the adjacent primary sections. The secondary turns with attached fins may be covered with thin insulation or left uninsulated, with the insulation on the primary sections to provide the required insulation betweenthe primary and secondary turns. In the latter case, the insulation covering for the primary turns should be carried the latter to pass in succession from one to another.

While there is herein disclosed by way of example several embodiments of the invention, it will be understood that wide departures from the form, relative arrangement and details of the parts as herein described may be made, all without departing from the spirit of the invention.

I claim:

1. A transformer having a plurality of serially connected primary winding sections, each section comprising one or a small plurality of turns in the form of a relatively wide thin flat conductor wound edgewise, said transformer having secondary turns connected in multiple each in the form of a relatively wide thin flat conductor also wound edgewise, there being one single secondary turn interleaved between each two adjacent primary sections and in close compact face-to-face relation thereto, separated only by intervening thin insulation.

2. A transformer having a plurality of serially connected primary winding sections, each section comprising a single turn in the form of a rela tively wide thin fiat conductor wound edgewise, said transformer having secondary turns connected in multiple each in the form of a relatively wide thin fiat conductor also wound edgewise, there being one single secondary turn interleaved between each two adjacent primary single-turn sections and in close compact face-to-face relation thereto, separated only by intervening thin insulation.

3. A transformer having a primary winding consisting of a relatively wide thin flat strip of conductive metal, folded on itself at spaced intervals, forming an edgewise wound helical winding providing a core space of polygonal crosssection, said transformer having secondary turns connected in multiple formed each from a relatively wide thin flat strip of conductive metal,

also folded on itself at spaced intervals to provide an edgewise-wound turn, there being a single secondary turn interleaved between adjacent primary turns and in close compact face-to-face relation thereto, separated only by intervening insulation 4; A transformer having a primary windingconsisting of a relatively wide thin flat strip of conductive metal, folded on itself at spaced intervals to form thereby an edgewise-wound helical winding, providing an enclosed core space of space, said transformer having secondary turns shaped each to provide a leg in the form of a, relatively wide thin flat conductor also wound edgewise, the projecting ends of the leg being connected in multiple, there being one single secondary leg interleaved between each two adjacent primary sections and in close compact overlying face-to-face relation thereto, separated only by intervening thin insulation.

'7. A transformerhaving a plurality of serially connected primary sections each comprising a relatively few helical turns each in the form of a relatively wide thin flat conductor Wound edgewise, said transformer having secondary turns connected in multiple in the form of a relatively wide thin flat conductor also wound edgewise, there being one single secondary tum interleaved between each two adjacent primary section and in close compact face-to-face relation thereto,

separated only by interleaving thin insulation, the

serially, connected terminal ends of successive primary sections extending for a substantial distance at one side of the transformer and clear wise, there being one single secondary turn interleaved between each two adjacent primary sections and in close compact face-to-face relation thereto, separated only by intervening thin insulation, and rejecting cooling fins attached to the outer edges of a plurality of said secondary turns intermediate the terminals thereof and containing each a cooling chamber for the circulation of a cooling medium.

9. A transformer having secondary windings consisting of a plurality of separate turns connected in multiple, each turn in the form of a single relatively wide thin fiat electrically unitary conductor wound edgewise and having attached to its outer edge at a point intermediate its length a projecting cooling fin containing a cooling chamber for the circulation of a cooling medium. I

10. A transformer having secondary windings consisting of a plurality of separate turns connected in multiple, each tm'n in the form of a single relatively wide thin flat electrically unitary conductor wound edgewise and having attached to its outer edge at a point intermediate its length a projecting cooling fin of substantially the same thickness as that of the conductor.

11'. A transformer having secondary turns in the form of a single relatively wide thin flat electrically unitary conductor wound edgewise, each such conductor comprising concentric inner and outer thin flat metal strips each wound on edge and closely lnterfitted radially and secured together to present a single conductive turn, the outer strip being substantially thicker than the inner one.

. CHARLES E. SEII'ERT. 

